Merge pull request #20008 from hcaseyal/update_docs

Add a developer trick to the installation doc, reorganize a bit

BUILDING.md

@@ -14,6 +14,7 @@ If you plan to build from source and run tests, install the following as well:
  $ [sudo] apt-get install libgflags-dev libgtest-dev
  $ [sudo] apt-get install clang libc++-dev
 ```
+Lastly, see the Protoc section below if you do not yet have the protoc compiler installed.
 
 ## MacOS
 
@@ -46,6 +47,7 @@ installed by `brew` is being used:
 ```sh
  $ LIBTOOL=glibtool LIBTOOLIZE=glibtoolize make
 ```
+Lastly, see the Protoc section below if you do not yet have the protoc compiler.
 
 ## Windows
 
@@ -112,6 +114,12 @@ From the grpc repository root
 ```sh
  $ make
 ```
+NOTE: if you get an error on linux such as 'aclocal-1.15: command not found', which can happen if you ran 'make' before installing the pre-reqs, try the following:
+```sh
+$ git clean -f -d -x && git submodule foreach --recursive git clean -f -d -x
+$ [sudo] apt-get install build-essential autoconf libtool pkg-config
+$ make
+```
 
 ## bazel